1. Field of the Invention
An apparatus and process for determining the effectiveness of metal stress-relief treatment.
2. Description of the Prior Art
Generally, when metals are shaped by bending or when metals are connected together by means such as welding, areas of high internal stress are created within the metal. If the stress is not relieved by, for example, heat treatment under controlled conditions or the like the metal is subject to severe corrosion in the area of high stress when placed in a conducting medium.
Metallic corrosion normally proceeds from areas of a metal which are more anodic than the surrounding areas of the metal to those areas that are less anodic. A concentration of internal stress within an area of a metal causes that area to be more anodic than the surrounding area. For example, when the end of a steel pipe is welded to a steel flange, high internal stresses are produced in the area of the weld (the heat-affected zone). Unless the steel pipe and flange thereafter are properly heat treated under controlled conditions, the steel pipe and flange will undergo severe corrosion at the heat-affected zone when the pipe is placed in a conducting medium. Such corrosion eventually will cause premature failure of the pipe.
The problem in reducing the effects of high internal stress in metals is monitoring or detection of the high stress area following a stress-relief treatment, such as heat treatment. This inventor knows of no prior art device which solves this problem short of metalurgical analysis involving complicated destructive sampling procedures.